1. Field of the Invention
The present invention relates to a flat panel display device and more particularly, to an organic electroluminescent display (ELD) device and method of fabricating the same.
2. Discussion of the Related Art
In general, organic electroluminescent display (ELD) devices have electron-input electrodes (cathodes) and hole-input electrodes (anodes). The electrons and the holes are input into light-emitting layers from the cathode and anode electrodes, respectively, thereby forming an exciton. The organic electroluminescent display (ELD) devices emit light when the exciton is reduced from an excited state level to a ground state level. Since the organic electroluminescent display (ELD) devices do not need additional light sources, as compared to thin film liquid crystal display (LCD) devices, volume and weight of the organic electroluminescent display (ELD) devices can be reduced. In addition, the organic electroluminescent display (ELD) devices are advantageous with respect to their lower power consumption, high luminance, fast response time, and low weight. Accordingly, the organic electroluminescent display (ELD) devices can be implemented in mobile telecommunication terminals, car navigation systems (CNGs), personal digital assistants (PDAs), camcorders, and palm computers. In addition, since manufacturing processes for the organic electroluminescent display (ELD) devices are simple, manufacturing costs can be reduced. The organic electroluminescent display (ELD) devices can be classified into passive matrix-type and active matrix-type devices. Although the passive matrix-type organic electroluminescent display (ELD) devices have simple structures and manufacturing processes are simplified, they require high power consumption and are not suitable for large-sized display devices. In addition, aperture ratios decrease as the number of conductive lines increase. On the other hand, the active matrix-type organic electroluminescent display (ELD) devices have high light-emitting efficiency and high image display quality.
FIG. 1 is cross sectional view of an organic electroluminescent display (ELD) device according to the related art. In FIG. 1, the organic electroluminescent display (ELD) device 10 has a transparent first substrate 12, thin film transistor array part 14, a first electrode 16, an organic light-emitting layer 18, and a second electrode 20, wherein the thin film transistor array part 14 is formed on the transparent first substrate 12. A first electrode 16, an organic light-emitting layer 18, and a second electrode 20 are formed over the thin film transistor array part 14, and the light-emitting layer 18 displays red (R), green (G), and blue (B) colored light, and is commonly formed by patterning organic material separately for each pixel for R (red), G (green) and B (blue). A second substrate 28 has a moisture absorbent desiccant 22. The organic electroluminescent display (ELD) device 10 is completed by bonding the first and second substrates 12 and 28 together by disposing a sealant 26 between the first and second substrates 12 and 28. The moisture absorbent desiccant 22 removes moisture and oxygen that may infiltrate into an interior of the organic electroluminescent display (ELD) device 10. The moisture absorbent desiccant 22 is formed by etching away a portion of the second substrate 28, filling the etched portion of the second substrate 28 with moisture absorbent desiccant material, and fixing the moisture absorbent desiccant material by tape 25.
FIG. 2 is a plan view of a thin film transistor array pixel part of an organic electroluminescent display (ELD) device according to the related art. In FIG. 2, the thin film transistor array part of the organic electroluminescent display (ELD) device has a switching element TS, a driving element TD, and a storage capacitor CST at every pixel region xe2x80x9cPxe2x80x9d that is defined on a substrate 12. The switching element TS and the driving element TD may be formed with combinations of more than two thin film transistors. The substrate 12 is formed of transparent material, such as glass and plastic. A gate line 32 is formed along a first direction, and a data line 34 is formed along a second direction perpendicular to the first direction. The data line 34 crosses the gate line perpendicularly with an insulating layer between the gate and data lines 32 and 34, and a power line 35 is formed along the second direction to be spaced apart from the data line 34. Thin film transistors are used for the switching element TS and the driving element TD, wherein the thin film transistor for the switching element TS has a gate electrode 36, an active layer 40, a source electrode 46, and a drain electrode 50, and the thin film transistor for the driving element TD has a gate electrode 38, an active layer 42, a source electrode 48, and a drain electrode 52. The gate electrode 36 of the switching element TS is electrically connected to the gate line 32, and the source electrode 46 of the switching element TS is electrically connected to the data line 34. The drain electrode 50 of the switching element TS is electrically connected to the gate electrode 38 of the driving element TD through a contact hole 54, and the source electrode 48 of the driving element TD is electrically connected to the power line 35 through a contact hole 56. The drain electrode 52 of the driving element TD is electrically connected to a first electrode 16 in the pixel regions xe2x80x9cP,xe2x80x9d and the power line 35 and a first capacitor electrode 15 formed of a polycrystalline silicon layer forms a storage capacitor CST.
FIG. 3 is a cross sectional view along IIIxe2x80x94III of FIG. 2 according to the related art. In FIG. 3, a buffer layer 14 is formed on a substrate 12 and a thin film transistor TD is formed on the buffer layer 14. The thin film transistor TD has a gate electrode 38, an active layer 42, a source electrode 56, and a drain electrode 52. An active layer 42 is formed on the buffer layer 14, and a second insulating layer 37 is formed on the active layer 42. A gate electrode 38 is formed on the second insulating layer 37, and third and fourth insulating layers 39 and 41 are sequentially formed over the gate electrode 38. The source and drain electrodes 56 and 52 are formed on the fourth insulating layer 41. A power line 35 is formed between the third and fourth insulating layers 39 and 41 to contact the source electrode 56. A fifth insulating layer 57 is formed on an entire surface of the substrate 12 on which the source and drain electrodes 56 and 52 are formed. A first electrode 16 is formed on the fifth insulating layer 57, and the first electrode 16 contacts the drain electrode 52 of the driving element. A light-emitting layer 18 that emits lights of specific wavelengths is formed on the first electrode 16, and a second electrode 20 is formed on the light-emitting layer 18. Before forming the light-emitting layer 18, a sixth insulating layer 58 is formed on the first electrode 16, and is patterned to expose a portion of the first electrode 16. The light-emitting layer 18 is formed on the exposed portion of the first electrode 16, and the second electrode 20 is formed over the entire substrate 12. A storage capacitor CST is formed in parallel with the driving element TD and uses a power line 35 as a first capacitor electrode and a polycrystalline silicon pattern 15 as a second capacitor electrode 20.
The organic electroluminescent display (ELD) device is commonly manufactured by forming the thin film transistor array part and the light-emitting part on a same substrate, and then bonding the substrate to an encapsulation. If the thin film transistor array part and the light-emitting part are formed on the same substrate, a yield of a panel having the thin film transistor array part and the light-emitting part is dependent upon the product of individual yields of the thin film transistor array part and an yield of the light-emitting part. Accordingly, the yield of the panel is greatly affected by the yield of the organic light-emitting layer. For example, if an inferior organic light-emitting layer, which is usually formed of a thin film of 1000 xc3x85 approximately, has a defect owing to impurities and contaminants even when the thin film transistor is formed well, the panel is classified as a inferior panel. This leads to a waste of money and material that are expended for manufacturing the satisfactory thin film transistor, and decreases the yield of the panel.
Bottom emission-type organic electroluminescent display (ELD) devices have advantageous high stability and variable fabrication processes. However, the bottom emission-type organic electroluminescent display (ELD) devices are not adequate for display devices that require high resolution since there is limit on increasing aperture ratio. In the top emission-type organic electroluminescent display (ELD) devices, light is emitted upward of the substrate. Since the light is emitted along an opposite direction of the thin film transistor in the top emission-type devices, the light can be emitted without influencing the thin film transistor array part that is positioned under the light-emitting layer, thereby simplifying design of the thin film transistor. In addition, the aperture ratio can be increased and the operational life span of the organic electroluminescent display (ELD) device can be increased. However, since a cathode is commonly formed over the light-emitting layer in top emission-type devices, material selection and light transmittance are limited, thereby lowering light transmission efficiency. Moreover, if a thin film-type passivation layer is formed to prevent reduction of the light transmittance, the thin film passivation layer may fail to prevent infiltration of exterior moisture and air from outside.
Accordingly, the present invention is directed to an organic electroluminescent display (ELD) device and method of fabricatng the same that substantially obviates one or more of problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an organic electroluminescent display (ELD) device in which a thin film transistor array part and a light-emitting part are independently formed on different substrates.
Another object of the present invention is to provide a method of fabricating an organic electroluminescent display (ELD) device in which a thin film transistor array part and a light-emitting part are independently formed on different substrates.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, an organic electroluminescent display (ELD) device includes a first substrate, a second substrate spaced apart and facing the first substrate, a plurality of switching thin film transistors and a plurality of driving thin film transistors interconnected on the first substrate, each of the switching thin film transistor and the driving thin film transistor having an active layer, a gate electrode, a source electrode, and a drain electrode, the drain electrode of the driving thin film transistor being extended to the pixel region to have an extended portion, a contact electrode contacting the extended portion of the drain electrode of the driving thin film transistor, a first electrode formed on the second substrate, an organic light-emitting layer on the first electrode, and a second electrode on the organic light-emitting layer.
In another aspect, A method of fabricating an organic electroluminescent display (ELD) device includes defining a plurality of pixel regions on first and second substrates, forming a plurality of switching thin film transistors and a plurality of driving thin film transistors interconnected on the first substrate, the switching thin film transistor and the driving thin film transistor each having an active layer, a gate electrode, a source electrode, and a drain electrode, the drain electrode of the driving thin film transistor being extended to the pixel region to have an extended portion, forming a contact electrode contacting the extended portion of the drain electrode of the driving thin film transistor, forming a first electrode on the second substrate, forming an organic light-emitting layer on the first electrode, forming a second electrode on the organic light-emitting layer, and bonding the first and second substrates so that the contact electrode of the first substrate contacts the second electrode.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.